AW: Minimoog Vcf

[Tony Allgood]

JH said:
>Better methods, if you don't have a reverse log pot:
(1) use a log slider pot and turn it upside down.
(2) use an ordinary log pot and connect it backward (ccw end
      position is max resonance). Relabel it as "damping" ...
(3) use an exponential VCA and a linear pot
(4) try to fif a shaft at the back of a log pot (reportedly works
      with the cheap plastic Piher types)



Are we talking about the emphasis pot here? Another way to get a really good
law is to use a 10K log pot as a potential divider. i.e.. the high Q end
(CW) to the ac coupled output of the diff amp and the low Q end (CCW) to
ground. The wiper is taken via another cap to the base of the bottom pair.
AND then connect the high Q end of the pot to the wiper via a 3K9 resistor.
This last addition gives a really smooooth change from no res to full
oscillation. Only one drawback is that control breakthrough gets worse...
but this is no problem if the VCF is pre-VCA.

Regards,

Tony Allgood, Cumbria, UK

e-mail: oakley at enterprise.net

Rack mounted Moog VCF module. Details to be found at...

http://aupe.phys.andrews.edu/diy_archive/schematics/effects/filter.html